1. Field of the Invention
The present invention relates to a mobile communication system and a mobile communication method. More specifically, the invention relates to a mobile communication system and a mobile communication method where a discrimination code specific to a mobile terminal is used as a discrimination code for a traffic channel of a forward channel and reverse channel transmitted between the mobile terminal and a mobile communication network.
2. Description of the Related Art
A well known system used in a mobile communication network composed of a mobile switching center, a base station control equipment and base stations is a mobile communication system which allows a mobile terminal to perform communications while moving in a service area provided by each base station by being connected through a radio channel.
Also, known as systems for multiplexing a radio channel between each base station and a plurality of mobile terminal so as to provide a multi-channel form are FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access) for spectrum-spreading an information bit to be communicated based on a diffusing code pattern composed of several tens of bits to several thousands of bits and then multiplexing the information bit in an identical frequency carrier wave.
In such various multiple access systems, each multiplexed channel is discriminated based on a time slot in the case of the TDMA system; based on a frequency in the case of the FDMA system (based on a frequency hopping pattern if a frequency hopping system is employed); and based on a diffusing code pattern in the case of the CDMA system, and even if a number of communications exist under the environment of the same time, the same space and the same frequency, individual communications are separated from others and thus communications can be carried out without being influenced by others.
For each of channels for performing such individual communications, an agreement is reached between a mobile terminal and a base station before communications are started, and thereafter communications are continued properly according to a mutual agreement under an existing state. For example, for hand-over processing carried out when a mobile terminal has moved from one base station to another and continues communications, a channel for performing communications with a new base station is newly decided as occasion demands, and the mobile terminal continues communications with the new base station of moving destination by using the decided channel.
A prior art of such a mobile communication system will be described by taking an example of IS-95 specification, which prescribes for a cellular mobile communication system using the CDMA system in North America.
For a so-called reverse channel, radio signals transmitted by a mobile terminal and received by a base station, used for separating from a reverse channel signal of another mobile terminal, modulation is performed by using a diffusing code based on an equipment number specifically allocated to each mobile terminal. This equipment number is a 32 bit number allocated by a terminal manufacturer to each mobile terminal and includes a manufacturer discrimination code and a serial number for each manufacturer, and this 32 bit number is a unique number. A diffusing code generated based on this equipment number has variations of 232 (4.2 billion).
On the other hand, a diffusing code for modulation performed for a forward channel, radio signals transmitted by a base station and received by a mobile terminal, is as follows. First, for means for discriminating each of a plurality of base stations existing in the mobile communication network, a group of 512 obtained by shifting PN (Pseudo Noise, pseudo random number group: 32768 chip length) by 64 chips is used as each base station signal diffusing code, and for means for separating signals of different mobile terminals in the same base station from one another, Walsh code is used. In other words, a signal transmitted from the base station to the mobile terminal is diffused and modulated by using these two kinds of codes (base station signal diffusing code, and Walsh code).
For performing communications between the mobile terminal and the base station by the CDMA system, received signals respectively transmitted therefrom must be oppositely-diffused for demodulation, and diffusing codes used for communications must be notified to each other beforehand. Thus, its method will be described.
First, after having entered a service area of a certain base station, the mobile terminal receives broadcast information of various kinds from the base station through a common channel, for which diffusing codes are predetermined by the system. Since the broadcast information contains diffusing code information of an access channel used for accessing the base station, the mobile terminal which requests call connection transmits a call connection request signal diffused and modulated based on the diffusing code thereof. In other words, a call connection request is made through the access channel. Since the call connection request signal contains an equipment number of the mobile terminal, the base station which has been on standby and received the call connection request from the mobile terminal through the access channel can be notified of a diffusing code used by the mobile terminal for a reverse channel based on the equipment number by referring to a data base of the base station control equipment or the mobile switching center.
Then, the base station control equipment or the mobile switching center selects a traffic channel to be used by the base station from resources, and reports a diffusing code (base station signal diffusing code and Walsh code) corresponding to the traffic channel allocated to the requested call from the base station to the mobile terminal. Accordingly, in the CDMA system, the diffusing code of the mobile terminal and the base station used for communications are notified to each other, and receiving preparations are made.
Furthermore, in hand-over processing for changing the base station to another during communications, the mobile terminal is notified of a diffusing code used for a forward channel of a base station as a hand-over destination, which is allocated by the base station control equipment or the mobile switching center, and communications with the base station as the hand-over destination are also started. After the mobile terminal has moved sufficiently away from the base station as a hand-over origin, the communications with this base station are cut off to perform communications only with the base station as the hand-over destination. Such soft hand-over processing is a characteristic art of the CDMA system.
As described above, a diffusing code for a reverse channel transmitted from the mobile terminal is specific to each mobile terminal, whereas a diffusing code for a forward channel transmitted from the base station to the mobile terminal is different for each base station. Thus, for switching of a radio channel following the movement of the mobile terminal from a certain base station area to another base station area, switching of a diffusing code for a reverse channel signal is not necessary, but regarding a diffusing code for a forward channel, it is necessary to select a forward channel diffusing code for a base station as an entering destination, allocate the diffusing code and notify the mobile terminal of the same.
Also, in the mobile terminal, it is necessary to receive traffic channel information used with a new base station for each movement between base station areas and form a speech channel which uses a new diffusing code.
The above processing needs operations of channel selecting, message editing, message transmitting and message transmission confirmation receiving to the network side device which includes the base stations, the base station control equipment and the mobile switching center, and operations of message receiving, message confirming, message transmission confirmation transmitting and speech channel forming to the mobile terminal, and thus from a system standpoint, influence of processing capability is given.
Therefore, in the conventional mobile communication system, since it was necessary to perform, for each movement of the mobile terminal between the base station areas, operations of message transmitting for specifying a diffusing code between the mobile terminal and the base station, confirming of transmission thereof, speech channel forming based on a new diffusing code, and so on, there was a problem of a load placed on processing capability. Especially, when the mobile terminal made repeated back and forth movement between the base station areas while performing packet communications, even if no transmitted burst data existed, only messages for channel allocation were passed around, which necessitated additional burdensome processing. Thus, a processing load placed in addition to the operations purely for communication purposes was a problem.
The present invention provides a mobile communication system and a mobile communication method where a discrimination code specific to a mobile terminal is used as a discrimination code for each of traffic channels of reverse channel and forward channel transmitted between the mobile terminal and a mobile communication network. The invention provides a mobile communication system and a mobile communication method, which enable the mobile terminal to conscientiously use the same channel without switching to a new channel even during a hand-over operation.
The present invention provides a mobile communication system and a mobile communication method, which can eliminate, in the case of the CDMA system, the necessity of message transmitting and receiving between a base station and a mobile terminal following switching of a diffusing code by using a mobile diffusing code as a diffusing code used for a traffic channel of a forward channel transmitted from the base station to the mobile terminal like that for a traffic channel of a reverse channel, and reduce a load for the above processing.
In the mobile communication system of the present invention for performing communications between a mobile terminal and a mobile communication network including a plurality of base stations and a base station control equipment, the mobile terminal includes a call connection requesting part for transmitting a call connection request signal through a predetermined control channel by adding specific information provided for the mobile terminal; a transmitting part for transmitting signals of a reverse channel based on a discrimination code specified by the specific information provided for the mobile terminal; and a receiving part for receiving signals of a forward channel based on a discrimination code specified by the specific information provided for the mobile terminal. The mobile communication network includes a translating part for translating the specific information provided for the mobile terminal, which is contained in the call connection request signal received through the control channel, and extracting a discrimination code for specifying each of the reverse channel and forward channel for the mobile terminal; a transmitting part for transmitting signals based on the discrimination code for specifying the forward channel, which is extracted by the translating part; and a receiving part for receiving signals based on the discrimination code for specifying the reverse channel, which is extracted by the translating part.
The mobile terminal further includes a monitoring part for measuring, based on information regarding each of the base stations adjacent to one another, which is notified beforehand, a receiving level of radio signals emitted from each of the adjacent base stations, and then reporting a measured result to the base station. The mobile communication network further includes a hand-over control part for notifying a base station of the discrimination codes for respectively specifying the reverse channel and forward channels used for communications with the mobile terminal, the base station being one where a receiving level of radio signals emitted from each of the adjacent base stations, which is reported from the mobile terminal, reaches a predetermined value, and then instructing starting of communications with the mobile terminal.
In the system for performing communications by the CDMA system, the mobile terminal includes a transmitting part for diffusing and modulating transmitted signals of a reverse channel going from the mobile terminal to a base station based on transmission diffusing code which is specified by specific information provided for the mobile terminal; and a receiving part for oppositely-diffusing and demodulating received signals of a forward channel going from a base station to the mobile terminal based on a receiving oppositely-diffusing code which is specified by the specific information provided for the mobile terminal. The mobile communication network includes a translating part for translating the specific information provided for the mobile terminal, which is contained in a call connection request signal received through a control channel, and extracting a diffusing code used for each of the reverse channel and forward channels for the mobile terminal; a transmitting part for diffusing and modulating transmitted signals based on the transmission diffusing code of the forward channel which is extracted by the extracting means; and a receiving part for oppositely-diffusing and demodulating received signals based on the receiving oppositely-diffusing code of the reverse channel which is extracted by the translating part.
In the mobile communication method of the present invention for performing communications between a mobile terminal and a mobile communication network including a plurality of base stations and a base station control equipment, the mobile terminal includes the followings:
(1) transmitting a call connection request signal through a predetermined control channel by adding specific information provided for the mobile terminal;
(2) transmitting signals of a reverse channel going from the mobile terminal to each of the base stations based on a discrimination code which is specified by the specific information provided for the mobile terminal;
(3) receiving signals of a forward channel going from each of the base stations to the mobile terminal based on a discrimination code which is specified by the specific information provided for the mobile terminal; and
(4) measuring, during communications, a receiving level of radio signals emitted from each of the adjacent base stations based on information regarding the base station, which is notified beforehand, and then reporting a measured result to the base station.
The method in the mobile communication network includes the followings:
(1) translating the specific information provided for the mobile terminal, which is contained in the call connection request signal received through the control channel, and extracting a discrimination code for specifying each of the reverse channel and forward channels for the mobile terminal;
(2) transmitting signals based on the extracted discrimination code which specifies the forward channel;
(3) receiving signals based on the extracted discrimination code which specifies the reverse channel; and
(4) notifying a base station of the discrimination codes for respectively specifying the reverse channel and forward channels for the mobile terminal, the base station being one where a receiving level of radio signals emitted from each of the adjacent base stations, which is reported from the mobile terminal, reaches a predetermined value, and then instructing starting of communications with the mobile terminal.
In the system for performing communications by the CDMA system, the mobile terminal of the mobile communication method of the present invention includes the followings:
(1) transmitting a call connection request signal through a predetermined control channel by adding specific information provided for the mobile terminal;
(2) diffusing and modulating transmitted signals of a reverse channel going from the mobile terminal to a base station based on a transmission diffusing code which is specified by the specific information provided for the mobile terminal;
(3) oppositely-diffusing and demodulating received signals of a forward channel going from a base station to the mobile terminal based on a receiving oppositely-diffusing code which is specified by the specific information provided for the mobile terminal; and
(4) measuring, during communications, a receiving level of radio signals emitted from each of the adjacent base stations based on information regarding the adjacent base station, which is notified beforehand, and then reporting a measured result to the base station.
The method in the mobile communication network includes the followings:
(1) translating the specific information provided for the mobile terminal, which is contained in the call connection request signal received through the control channel, and extracting a diffusing code used for each of the reverse channel and forward channel for the mobile terminal;
(2) diffusing and modulating transmitted signals based on the extracted transmission diffusing code of the forward channel;
(3) oppositely-diffusing and demodulating the extracted receiving oppositely-diffusing code of the reverse channel; and
(4) notifying a base station of the reverse channel oppositely-diffusing code and the forward channel diffusing code for the mobile terminal, the base station being one where a receiving level of radio signals emitted from each of the adjacent base stations, which is reported from the mobile terminal, reaches a predetermined value, and then instructing starting of communications with the mobile terminal.